sched_ext: Maintain an online cid mask in the scheduler arenagrafted

Schedulers on the default cid mapping treat [0, nr_online_cids) as the
online set and restart on hotplug. Schedulers that install their own mapping
with scx_bpf_cid_override() have no way to learn which cids are online: the
count no longer identifies members and the CPU-form cpumask is unusable from
cid programs. This is an obvious hole in the cid API.

Add scx_bpf_online_cmask(), a kernel-maintained cmask in the scheduler's
arena, allocated alongside the per-CPU scratch masks and populated after the
cid mapping is finalized and before ops.init(), for child schedulers too.
The pointer stays valid through ops.exit() with no reference to take. It is
the arena offset as a void pointer, the same form struct_ops arena arguments
arrive in. The verifier types the void return as a scalar for the program's
arena cast.

The mask follows the SCX hotplug notifications: seeded from cpu_active_mask
and updated before ops.cid_online/offline() runs, so it lags cpu_online_mask
only inside a hotplug transition. Updates walk the scheduler list under the
lock that also serializes unlinking. Reads are live, not atomic snapshots.
Root initialization excludes hotplug.

v2: Reworded the getter kerneldoc (Andrea Righi).

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>

1 files changed, 289 insertions, 0 deletions

diff --git a/tools/perf/util/values.c b/tools/perf/util/values.c
new file mode 100644
index 000000000..6eaddfcf8
--- /dev/null
+++ b/tools/perf/util/values.c
@@ -0,0 +1,289 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <inttypes.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+#include <linux/zalloc.h>
+
+#include "values.h"
+#include "debug.h"
+#include "evsel.h"
+
+int perf_read_values_init(struct perf_read_values *values)
+{
+	values->threads_max = 16;
+	values->pid = calloc(values->threads_max, sizeof(*values->pid));
+	values->tid = calloc(values->threads_max, sizeof(*values->tid));
+	values->value = calloc(values->threads_max, sizeof(*values->value));
+	if (!values->pid || !values->tid || !values->value) {
+		pr_debug("failed to allocate read_values threads arrays");
+		goto out_free_pid;
+	}
+	values->threads = 0;
+
+	values->counters_max = 16;
+	values->counters = malloc(values->counters_max * sizeof(*values->counters));
+	if (!values->counters) {
+		pr_debug("failed to allocate read_values counters array");
+		goto out_free_counter;
+	}
+	values->num_counters = 0;
+
+	return 0;
+
+out_free_counter:
+	zfree(&values->counters);
+out_free_pid:
+	zfree(&values->pid);
+	zfree(&values->tid);
+	zfree(&values->value);
+	return -ENOMEM;
+}
+
+void perf_read_values_destroy(struct perf_read_values *values)
+{
+	int i;
+
+	if (!values->threads_max || !values->counters_max)
+		return;
+
+	for (i = 0; i < values->threads; i++)
+		zfree(&values->value[i]);
+	zfree(&values->value);
+	zfree(&values->pid);
+	zfree(&values->tid);
+	zfree(&values->counters);
+}
+
+static int perf_read_values__enlarge_threads(struct perf_read_values *values)
+{
+	int nthreads_max = values->threads_max * 2;
+	void *npid = realloc(values->pid, nthreads_max * sizeof(*values->pid)),
+	     *ntid = realloc(values->tid, nthreads_max * sizeof(*values->tid)),
+	     *nvalue = realloc(values->value, nthreads_max * sizeof(*values->value));
+
+	if (!npid || !ntid || !nvalue)
+		goto out_err;
+
+	values->threads_max = nthreads_max;
+	values->pid = npid;
+	values->tid = ntid;
+	values->value = nvalue;
+	return 0;
+out_err:
+	free(npid);
+	free(ntid);
+	free(nvalue);
+	pr_debug("failed to enlarge read_values threads arrays");
+	return -ENOMEM;
+}
+
+static int perf_read_values__findnew_thread(struct perf_read_values *values,
+					    u32 pid, u32 tid)
+{
+	int i;
+
+	for (i = 0; i < values->threads; i++)
+		if (values->pid[i] == pid && values->tid[i] == tid)
+			return i;
+
+	if (values->threads == values->threads_max) {
+		i = perf_read_values__enlarge_threads(values);
+		if (i < 0)
+			return i;
+	}
+
+	i = values->threads;
+
+	values->value[i] = calloc(values->counters_max, sizeof(**values->value));
+	if (!values->value[i]) {
+		pr_debug("failed to allocate read_values counters array");
+		return -ENOMEM;
+	}
+	values->pid[i] = pid;
+	values->tid[i] = tid;
+	values->threads = i + 1;
+
+	return i;
+}
+
+static int perf_read_values__enlarge_counters(struct perf_read_values *values)
+{
+	int counters_max = values->counters_max * 2;
+	struct evsel **new_counters = realloc(values->counters,
+					     counters_max * sizeof(*values->counters));
+
+	if (!new_counters) {
+		pr_debug("failed to enlarge read_values counters array");
+		goto out_enomem;
+	}
+
+	for (int i = 0; i < values->threads; i++) {
+		u64 *value = realloc(values->value[i], counters_max * sizeof(**values->value));
+
+		if (!value) {
+			pr_debug("failed to enlarge read_values ->values array");
+			goto out_free_counters;
+		}
+
+		for (int j = values->counters_max; j < counters_max; j++)
+			value[j] = 0;
+
+		values->value[i] = value;
+	}
+
+	values->counters_max = counters_max;
+	values->counters = new_counters;
+
+	return 0;
+out_free_counters:
+	free(new_counters);
+out_enomem:
+	return -ENOMEM;
+}
+
+static int perf_read_values__findnew_counter(struct perf_read_values *values,
+					     struct evsel *evsel)
+{
+	int i;
+
+	for (i = 0; i < values->num_counters; i++)
+		if (values->counters[i] == evsel)
+			return i;
+
+	if (values->num_counters == values->counters_max) {
+		int err = perf_read_values__enlarge_counters(values);
+
+		if (err)
+			return err;
+	}
+
+	i = values->num_counters++;
+	values->counters[i] = evsel;
+
+	return i;
+}
+
+int perf_read_values_add_value(struct perf_read_values *values,
+				u32 pid, u32 tid,
+				struct evsel *evsel, u64 value)
+{
+	int tindex, cindex;
+
+	tindex = perf_read_values__findnew_thread(values, pid, tid);
+	if (tindex < 0)
+		return tindex;
+	cindex = perf_read_values__findnew_counter(values, evsel);
+	if (cindex < 0)
+		return cindex;
+
+	values->value[tindex][cindex] += value;
+	return 0;
+}
+
+static void perf_read_values__display_pretty(FILE *fp,
+					     struct perf_read_values *values)
+{
+	int i, j;
+	int pidwidth, tidwidth;
+	int *counterwidth;
+
+	counterwidth = malloc(values->num_counters * sizeof(*counterwidth));
+	if (!counterwidth) {
+		fprintf(fp, "INTERNAL ERROR: Failed to allocate counterwidth array\n");
+		return;
+	}
+	tidwidth = 3;
+	pidwidth = 3;
+	for (j = 0; j < values->num_counters; j++)
+		counterwidth[j] = strlen(evsel__name(values->counters[j]));
+	for (i = 0; i < values->threads; i++) {
+		int width;
+
+		width = snprintf(NULL, 0, "%d", values->pid[i]);
+		if (width > pidwidth)
+			pidwidth = width;
+		width = snprintf(NULL, 0, "%d", values->tid[i]);
+		if (width > tidwidth)
+			tidwidth = width;
+		for (j = 0; j < values->num_counters; j++) {
+			width = snprintf(NULL, 0, "%" PRIu64, values->value[i][j]);
+			if (width > counterwidth[j])
+				counterwidth[j] = width;
+		}
+	}
+
+	fprintf(fp, "# %*s  %*s", pidwidth, "PID", tidwidth, "TID");
+	for (j = 0; j < values->num_counters; j++)
+		fprintf(fp, "  %*s", counterwidth[j], evsel__name(values->counters[j]));
+	fprintf(fp, "\n");
+
+	for (i = 0; i < values->threads; i++) {
+		fprintf(fp, "  %*d  %*d", pidwidth, values->pid[i],
+			tidwidth, values->tid[i]);
+		for (j = 0; j < values->num_counters; j++)
+			fprintf(fp, "  %*" PRIu64,
+				counterwidth[j], values->value[i][j]);
+		fprintf(fp, "\n");
+	}
+	free(counterwidth);
+}
+
+static void perf_read_values__display_raw(FILE *fp,
+					  struct perf_read_values *values)
+{
+	int width, pidwidth, tidwidth, namewidth, rawwidth, countwidth;
+	int i, j;
+
+	tidwidth = 3; /* TID */
+	pidwidth = 3; /* PID */
+	namewidth = 4; /* "Name" */
+	rawwidth = 3; /* "Raw" */
+	countwidth = 5; /* "Count" */
+
+	for (i = 0; i < values->threads; i++) {
+		width = snprintf(NULL, 0, "%d", values->pid[i]);
+		if (width > pidwidth)
+			pidwidth = width;
+		width = snprintf(NULL, 0, "%d", values->tid[i]);
+		if (width > tidwidth)
+			tidwidth = width;
+	}
+	for (j = 0; j < values->num_counters; j++) {
+		width = strlen(evsel__name(values->counters[j]));
+		if (width > namewidth)
+			namewidth = width;
+		width = snprintf(NULL, 0, "%x", values->counters[j]->core.idx);
+		if (width > rawwidth)
+			rawwidth = width;
+	}
+	for (i = 0; i < values->threads; i++) {
+		for (j = 0; j < values->num_counters; j++) {
+			width = snprintf(NULL, 0, "%" PRIu64, values->value[i][j]);
+			if (width > countwidth)
+				countwidth = width;
+		}
+	}
+
+	fprintf(fp, "# %*s  %*s  %*s  %*s  %*s\n",
+		pidwidth, "PID", tidwidth, "TID",
+		namewidth, "Name", rawwidth, "Raw",
+		countwidth, "Count");
+	for (i = 0; i < values->threads; i++)
+		for (j = 0; j < values->num_counters; j++)
+			fprintf(fp, "  %*d  %*d  %*s  %*x  %*" PRIu64,
+				pidwidth, values->pid[i],
+				tidwidth, values->tid[i],
+				namewidth, evsel__name(values->counters[j]),
+				rawwidth, values->counters[j]->core.idx,
+				countwidth, values->value[i][j]);
+}
+
+void perf_read_values_display(FILE *fp, struct perf_read_values *values, int raw)
+{
+	if (raw)
+		perf_read_values__display_raw(fp, values);
+	else
+		perf_read_values__display_pretty(fp, values);
+}